The aim of this study was to evaluate the efficacy of a brief motivational enhancement therapy in reducing cannabis use and cannabis-related problems in a population of non-treatment-seeking adolescent cannabis users. In a randomized controlled trial, 40 young people (aged 14-19 years) were randomly assigned to either a two-session brief intervention or a 3-month delayed-treatment control condition. The intervention consisted of a detailed assessment and a session of motivational enhancement therapy. An additional optional discussion of skills for reducing or quitting cannabis use was offered if a participant was interested in discussing these issues. Primary outcome measures were changes in days of cannabis use, mean quantity of cannabis used weekly, and number of Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition dependence symptoms reported. Significantly greater reductions on these measures were found in the Adolescent Cannabis Check-up group at 3-month follow-up. Between-group effect sizes were moderate. The approach is acceptable to participants and merits further evaluation with this difficult to reach population.